Anticorrosive behavior of hydroxyapatite as an environmentally friendly pigment

From the point of view of waste recycling, hydroxyapatite (HAp) can be synthesized using the waste sludge from semiconductor process. The possibility of using HAp as an anticorrosive pigment was investigated. The water absorption of coating pigmented with anticorrosive pigment, HAp, red lead (RL) and zinc potassium chromate (ZPC), and the corrosion at interface between coating and substrate were monitored using AC impedance technique. The amount of absorbed water decreased in the order of ZPC- > HAp- > RL-pigmented > unpigmented film. However, the water absorbed into HAp- or ZPC-pigmented film seems to be beneficial to anticorrosive function. The anticorrosive performance of HAp is superior or at least comparable to those of ZPC and RL, which have been known as representative anticorrosive pigments. It seems that the anticorrosive properties of HAp is mainly achieved by passivating the substrate, namely the soluble component of HAp reacts with Fe to form iron phosphate in the presence of water. (C) 2002 Elsevier Science Ltd. All rights reserved.